In recent years, the number of so-called individually designed spectacle lenses has been significantly increasing. These individually designed spectacle lenses take into account a number of individual parameters of an intended wearer. This leads towards more and more lenses being designed with “free form surfaces,” i.e., surfaces that do not inhibit any symmetry any more or are not restricted by any symmetry requirements. A full surface profile is determined, for example by providing sagitta for each surface over the whole area, and forwarded to a manufacturing site, for example for grinding, polishing, coating, and/or edging.
Prescription sunglasses for large wrapped frames suffer from cosmetic limitations for stronger prescriptions, and the delivery ranges are limited due to the thickness limitations of the puck, i.e., the uncut finished spectacle lens. This is particularly a problem for the myopic prescriptions, where the temporal edge thickness can get quite high for fairly moderate minus prescriptions, e.g., sphere powers smaller than −2.00 diopters may give maximum edge thickness of larger than 5 mm in large frames. It is also a problem for the higher plus prescriptions where the need to have a certain minimum edge thickness may lead to high values of center thickness. Furthermore, in some of the semi-rimless styles of wrapped frames (e.g., the so-called “blade frames”) any differences in the thickness profiles in the two lenses making a pair become quite obvious and are considered undesirable by wearers wishing to see their eyewear more symmetrical. A known solution to this problem has been to use spherical or toric shaped carrier surfaces that had a step change in slope and curvature across the boundary between the central prescription zone and peripheral temporal zone. This approach required a two-pass surfacing process and was not compatible with the free-form soft pad polishing tools being currently used by the lens surfacing industry.
Early attempts to introduce a blended carrier based on the disclosures of document WO 97/35224 were not well tolerated by wearers and were abandoned. There was no provision for edge thickness difference reduction between a pair of lenses for the two eyes, and this method was not flexible enough to lend itself to such application. Unlike WO 97/35224, the carrier surface needs to be applied to both single vision and progressive lens surfaces.
Further reference is made to US patent application publication 2015/0338680 A1 of the same applicant and published on Nov. 26, 2015, showing a computer-implemented method for providing a modified lens shape for an uncut lens blank.
Further documents related to lens design are WO 03/050596 A1, WO 04/029694 A1; US 2007/008488 A; US 2005/206840 A; US 2005/225719 A; US 2006/274258 A; US 2008/024719 A; US 2008/284978 A; WO 08/135178 A1; US 2012/008089 A; US 2010/296048 A; US 2011/134388 A; U.S. Pat. Nos. 7,070,274 B2; 7,445,333 B2; 7,527,376 B2; 8,002,404 B2; 8,118,425 B2; 8,449,111; 4,561,736 A and US 2013/107205 A.
Based on this, it is an object of the current disclosure to overcome the above issues.